Existing press technologies essentially are divided into two types--(1) day light presses, where pressing is done between two rigid plates; and (2) diaphragm presses, also known as membrane or membraneless presses, where an object or workpiece is pressed between a flexible surface and a rigid plate or between two flexible surfaces. In membrane presses the membrane seals a pressurizable chamber. When the chamber is pressurised the membrane conforms to the shape of the workpiece. Additionally vacuum may be applied to the other side of the workpiece via a vented lower platen.
As the size of the object or workpiece increases it becomes more difficult to maintain quality. This is reflected by the increasing rate of rejects caused by unrepairable creases or wrinkles in the surface finish applied by the diaphragm press. The increase in rejection rate is a significant economic cost. Instances where the risk of creasing or wrinkling is high include medium to large workpieces (eg 1200 mm-2400 mm or longer), irregular or perforated components (eg frames), thermofoils which are unstable when exposed to heat due to type, gauge, or the release of captive process stresses, hygroscopic materials which become unstable when in contact with a wet, water-based glue line (which causes undulations) (eg veneers or paper), and free standing components which must be straight after process curing temperatures and heat resistance have been achieved (eg 2400 mm high pantry doors or panels).
Present day diaphragm presses do not offer a membrane that can be either flexible or rigid. We have discovered that it is possible to provide a membrane that can be flexible or rigid as required. We have achieved this by installing, on the side of the membrane remote from the workpiece, a platen assembly which can be moved independently of and relative to the combination frame (also known as an "L" frame) and/or other frames, trays, tables, or conveyors of the press and which can bring the membrane into contact with the workpiece. Such a platen assembly may include a vented heating plate allowing the application of heat and pressure to the workpiece via the membrane as required. Parts of the surfaces of the platen assembly of the invention and the combination frame make positive contact when the platen assembly is retracted and are held or locked together to establish a seal. This results in re-establishment of the chamber of the press, and the press then functions as a normal diaphragm press in which heat, pressure and vacuum can be applied in accordance with current technology.
Thus, according to one aspect of the present invention there is provided a multi-function diaphragm press including upper and lower platen assemblies separated by a flexible membrane, one of said platen assemblies being movable between a first position whereby said one of said platen assemblies does not contact said flexible membrane and a second position whereby said flexible membrane is in contact with said one of said platen assemblies to provide a rigid membrane. Preferably said one of said platen assemblies is moved by hydraulic means.
Preferably said one of said platen assemblies can be installed in either the top or the bottom half of the press. Alternatively, two independently movable platen assemblies can be installed in the press, one in either half. It is also possible that more than one independently movable platen assembly may be installed in either half of the press.
Preferably each platen assembly includes a plate, hereinafter called a bolster, a heating means and a vented heat exchanging means. Preferably the plate is made of steel.
Where an independently movable platen assembly is installed in the top half of a diaphragm press it provides a rigid surface adjustable by raising or lowering the platen assembly in the top half of the normally flexible press without the need to remove or add parts to the press. Retraction, sealing and/or locking of the independently movable platen assembly against the combination frame lip permits normal diaphragm press operation.
A significant advantage is that a workpiece can be flat surface-pressed with the rigid surface provided by the lowered independently movable platen assembly and, if required, flexibly 3-D pressed immediately afterward. This is particularly useful for pressing large or unusual objects or where the surface coating materials vary in type, gauge, thermal stability or memory effects or where instability affects flatness such as where a hygroscopic material like veneer contacts a wet glue line. A significant reduction in losses due to creasing of surface coatings during the pressing process can be achieved by rigid membrane flat pressing of surface coating to flat surfaces of the object or workpiece prior to a rapid changeover to flexible 3-D pressing to complete the forming and bonding of the surface coating to the surfaces of the object or workpiece.